The present invention relates to actuator apparatus and in particular, but not exclusively, to hydraulic apparatus for installing or extracting pile elements and like members by vibration or impact.
The apparatus may be used with pile elements as defined in British Standard specification BS EN 996; 1996 entitled xe2x80x9cPiling Equipmentxe2x80x94Safety Standardsxe2x80x9d. Piles and like members are driven into the ground for a variety of reasons in the construction industry and other industries. In addition to pile elements as defined in BS EN 996, other types of element are conventionally installed in a similar manner, such as steel trench sheeting, and PVC, polystyrene and glass fibre composite piles. These may be used for shoring up a trench wall, protection against erosion, etc. Devices may also be driven in a similar manner for soil compaction.
For simplicity, the single term xe2x80x9cpile elementxe2x80x9d is used in a broader manner in this specification than in BS EN 996, in order to encompass all of these alternatives and similar items drivable into the ground. In addition, apparatus may be used to withdraw members from the ground by applying forces in the opposite direction. Again for simplicity, the term xe2x80x9cinstallationxe2x80x9d is used herein to refer to the application of forces for causing items to be forced down against resistance provided by the ground, or to penetrate the ground, xe2x80x9cextractionxe2x80x9d is used to refer to the application of forces for causing items to be withdrawn from the ground, and xe2x80x9cdrivingxe2x80x9d is used to refer to installation and extraction.
Various devices have been proposed for providing driving forces, by vibration, impact or the application of static forces. The nature and magnitude of forces to be used will in practice be chosen according to a number of factors, including the soil type and the nature of the pile element being driven. For instance, in loose, non-cohesive soils, vibration is often the quickest and quietest technique. Relatively high frequency vibration is generally attenuated more quickly and is therefore preferable for use near populated areas, particularly brown field sites. Other soil types are better served by impact driving, but this can cause problems from noise and shock waves. Legislation, particularly concerning health and safety, is becoming increasingly strict in respect of vibration and noise created by piling operations, and this presents a further factor influencing the choice of technique.
It is therefore conventional to build apparatus in a variety of different sizes and operating in a variety of different ways, so that an appropriate apparatus can be chosen for a particular situation. Unfortunately, problems with delay can then occur if it is found that the choice was inappropriate. Alternatively, equipment may be provided unnecessarily, so that alternatives are available on-site if required, but remain unused if not.
The present invention seeks to obviate or mitigate these or other disadvantages of the prior art.
The invention provides actuator apparatus comprising piston means operable to create driving forces from a supply of pressurised fluid, and valve means operable to supply pressurised fluid to the piston means according to a predetermined sequence, to cause the apparatus to execute a first operation, the valve means and the piston means being housed within a common member, and the apparatus being characterised in that the valve means or the piston means or both being removable from the member for replacement by an alternative means operable within the common member to cause the apparatus to execute an alternative operation, and wherein the or each valve means comprise a valve arrangement rotatable within a housing, there being ports in the housing walls for pressurised fluid, and the valve arrangement carrying partitions which serve to change the connections between the fluid ports in accordance with the predetermined sequence as the valve arrangement rotates, and wherein the valve arrangement of the or at least one of the valve means is axially movable to change the predetermined sequence.
We have realised that an actuator according to the invention can be used to apply vibration, impact or static forces to pile elements and also to tooling such as a compaction plate, an auger or mandrel, or demolition shears or cutters. Preferably the valve means is removable for replacement with an alternative valve means operable to supply fluid according to an alternative sequence. The valve arrangement may have a first axial position at which a wider fluid path is provided to one face of the piston means than to the other, and be movable to a second axial position at which a narrower fluid path is provided to the said one face than to the other. The valve means may have a port having a width which is not constant in the axial direction of the valve arrangement, whereby the effective width of the fluid path to the piston means can be set by setting the axial position of the valve arrangement. The valve arrangement may provide drive alternatively to opposite faces of a piston of the piston means, whereby to create reciprocation.
The valve arrangement may be formed to complete a plurality of cycles of the piston means for each full turn of the valve arrangement. The valve arrangement may have a first axial position in which a first number of cycles are completed for each full turn of the valve arrangement and a second axial position in which a different number of cycles is completed for each full term. The fluid path to the piston means may be relatively narrow in the first axial position, and relatively wide in the second axial position.
The apparatus may further comprise intermediate means to which driving forces are provided by the piston means, and which convey driving forces to an item being driven. The item may be an item of tooling or a pile element. The intermediate member may provide for movement to align the tooling and may be operable hydraulically or pneumatically. The intermediate member may convey forces to clamping members by which a workpiece may be clamped. The clamping members preferably extend at an angle to the intermediate means to allow side or end clamping of a workpiece. The intermediate means is preferably elongate, and preferably extends to one side of the common member. The clamping members may extend substantially perpendicular to the intermediate means.
The intermediate means may extend through a passage within the piston means, and have one or more enlarged heads against which the piston means may act in either of two opposite directions.
Resilient members may be provided, against which the piston means acts, in use. The piston means may be isolated by the resilient members from direct impacts, whereby to create vibrating driving forces. The piston means may create impact forces when the resilient members become fully compressed.
The apparatus is preferably adapted for resilient attachment to a mounting bracket by means of which the apparatus may be supported by a conventional support arrangement. The support arrangement may be provided on a support machine, preferably operable to apply crowd forces to the apparatus and preferably able to supply pressurised fluid to the apparatus.